The invention relates to a communication system and in particular a method and system for adjusting the transmitter power levels within that communication system.
This invention relates to a 3G cellular communication system and in particular the Frequency Division Duplex or Time Division Duplex (FDD/TDD) mode of the Wideband Code Division Multiple Access (WCDMA) system defined by the Third Generation measurement processor Partnership Project (3GPP). This is described in more detail at www.3gpp.org.
The 3G cellular communication system provides subscribers with the ability to transmit text, digitised voice, video and other multi-media data from their mobile handset. The system is presently implemented by the Universal Mobile Telecommunications System (UMTS) which builds on the existing Global System for Mobile Communications (GSM) network and General Packet Radio Service (GPRS) technology. The initial specification for UMTS were referred to as ‘Release 99’, (R99) and define the standard network architecture for UMTS systems. More recently ‘Release 5’ (R5) has been developed, expanding the Release 99 functionality to include The IP Multimedia Subsystem (IMS). This provides an all Internet Protocol based wireless network, in comparison to the separate voice, data, signalling, and control network elements of Release 99 systems. Release 99 and Release 5 architecture will now be described in more detail by way of background and with reference to FIG. 1.
The circuit switched (CS) domain 2 of the Release 99 architecture is illustrated in the lower part of FIG. 1. User Equipment (UE) 4 will normally connect to the Node B 6, the Node B to the Radio Network Controller (RNC) 8 and the RNC to a Mobile Switching Centre (MSC) 10 in this case the MSC_B. The MSC allows interconnection to other networks and to the Public Switched Telephone Network (PSTN) 12. The MSC_B has access to the home location register (HLR) 14 and to the Authentication Centre (AuC) via the HLR.
The upper half of FIG. 1 illustrates the Release 5 IMS network architecture 20. In addition to the Node B 22 and the RNC 24, there is the Packet Switched PS domain Serving GPRS Support Node and Gateway GPRS Support Node (SGSN/GGSN) 26 and the IMS specific components such as Proxy-Call Session Control Function (P-CSCF) 28, Serving-Call Session Control Function (S-CSCF) 30, the Home Subscriber Server (HSS) 32, the Media Gateway Control Function (MGCF) 34 and the media gateway (MGW) 34 which connects to the PSTN 36.
The media sessions are established from the UE 4 via the PS domain and the P-CSCF and the S-CSCF. If the media session is via an external network such as the PSTN or another Public Land Mobile Network (PLMN) then the MGCF and the MGW are also required. The structure and operation of the IMS within the R5 network architecture are well known by those skilled in the art and are defined in the 3GPP specifications TS23.002, TS24.228 and TS24.229.
In addition to the above described elements, FIG. 1 illustrates a Local Network Node (LNN) 40, developed by the applicants, which provides supplemental controlled access to the Release 99 and Release 5 network architectures bypassing Node B's 6 and 22. The LNN is described in more detail in the applicant's co-pending patent application entitled “Local Network Node”.
As mentioned above, the UE 4 normally connects to the network via Node B typically co-located with a Base Transceiver Station of the underlying GSM system. The LNN however provides a local user-controlled access point for the network, that may be installed in the home or office. By means of the LNN, a user can regulate local subscribers' access to the network.
Essentially, the LNN is a composite of elements of a Node B, an RNC, MSC, SGSN, GGSN and P-CSCF. In order to accommodate the LNN in the Release 99 architecture, the SIP/MSC_A element 16 is provided, logically connected to MSC_B 10, HLR/AuC 14 and PSTN 12. The SIP/MSC_A is configured to convert the Session Initiation Protocol commands from the UE 4, which are used to establish a session on an IP network, and to the ISND User part (ISUP/SS7) messages used to manage calls over a PSTN, and vice versa.
Thus, where a LNN is installed, the UE will connect to the Release 99 network via the LNN and SIP/MSC_A element 16, and to the Release 5 architecture via the LNN and S-CSCF 30.
At the interface to the R99 network, the UE will look like an SIP client that establishes circuit switched connections to the SIP enabled MSC, using the SIP signalling protocol. The SIP messages are used to transport the circuit switched signalling messages to the MSC, which then looks like an MSC as far as the remainder of the external network is concerned.
At the interface between the LNN 40 and the S-CSCF 30, the LNN looks like a UE communicating with the S-CSCF through a P-CSCF. Preferably, the messages from the LNN to the S-CSCF conform with the interface defined within the 3gpp specifications. The decision as to which network architecture the LNN will connect to is an operator decision. It may be the R99 circuit switched architecture, or it may be the R5IMS architecture.
As mentioned earlier the LNN is intended for local installation in the home or office for example. In general, the coverage area of the LNN cell, hereafter referred to as a pico-cell, will overlap with the overlaying network cell hereafter referred to as a macro-cell. In addition, it is likely that the pico-cell will operate on the same frequency as the macro-cell for reasons of frequency economy.
The deployment of the pico-cells will occur in an un-coordinated and ad-hoc fashion as LNNs are installed to meet user requirements. The power levels of the pico-cells will need to be high enough for satisfactory connection with the local UEs. In this arrangement, the downlink transmissions from the pico-cell will interfere with the downlink transmissions from the macro-cell, and the interference is likely to result in degradation in the coverage of the macro-cell. We have therefore appreciated that it is desirable to regulate the power of the signals transmitted by the LNN.